1. Field of Invention
The present invention relates to an integrated circuit and a method of fabricating the same; more particularly, the present invention relates to a semiconductor device and a method of fabricating the same.
2. Description of Related Art
With the development of technology in electronic equipments for communication, etc., the operating speed of a transistor increases rapidly. However, limited by the mobility of electrons and holes in the silicon channel, the area of application of a transistor is limited.
Altering the mobility of electrons and holes in the channel by controlling the mechanical stress in the channel is one approach to enhance the operational speed of a transistor.
Conventionally, the silicon germanium (SiGe) type of material has been proposed for forming the source/drain regions of the transistor, wherein portions of the substrate designated for forming the source/drain regions are removed. Thereafter, a selective area epitaxial growth technique is applied to fill the substrate with silicon germanium. Since germanium has a larger atom size to impose a compressive stress to the channel, using a silicon germanium material for the source/drain regions enhances the mobility of holes, when compared with a silicon material. Another approach is by using silicon nitride as a contact etching stop layer (CESL) to generate stress for influencing the driving current of the transistor. As a result, the efficiency of the device is increased. This technique is known as local mechanical-stress control.
According to the typical local mechanical-stress control method, a strain layer is applied to cover the transistor and it's peripheral. For example, in a complementary metal oxide semiconductor device, a tensile film is normally applied to cover the n-type channel metal oxide semiconductor device region, while a compressive film is applied to cover the p-type channel metal oxide semiconductor device region. However, the increase of the driving current by a single strain layer is very limited. Hence, to enhance the efficiency of the device becomes restricted.